Not everyone has the ability to just draw their own clipart if they can’t find what they need quickly. That is a blessing that I’ve enjoyed too many times to count. However, even an artist would like a different take on a topic through a photograph or other graphical representation.
To help you along, I’d like to suggest that besides the free clipart websites that you have already most likely searched through, and been disappointed in, that you can either ask for friends and family for certain photographs that they might have on hand. If you do that, be CERTAIN to get their permission to use their photo in writing, to avoid any problems later on.